Operation of all integrated circuits (ICs) depends upon a power supply having a potential difference for use in powering internal integrated circuit components to ensure their operation. It is common for the power supply battery to be inadvertently reversed, thereby reversing the bias of the applied potential difference. In the automotive industry, for example, during a jump start, a battery may be mistakenly connected backwards to a circuit wherein the negative supply connects to the positive power rail and the positive supply connects to the negative power rail. As a result, severe damage to integrated circuits connected to the power supply occurs without any form of reverse bias protection between the integrated circuit and the applied potential difference. Moreover, this extreme condition of reverse battery can cause excessive power consumption.
There, however, are numerous ways that reverse bias protection may be implemented within an integrated circuit design. Common reverse bias protection circuitry include current-limiting resistors, diodes or MOS-transistors in series with a big pass transistor. Big pass transistors are used in integrated circuit design to enable a large flow of current within the integrated circuit. Yet, during the reverse bias condition, damage will result. Thus, these components may be connected in series with the big pass transistor for protection. These components, however, tend to pass the same amount of large current as the big pass transistor. Thereby, current-limiting resistors, diodes and MOS transistors connected in series with the big pass transistor may cause undesired voltage drops.
For example a known reverse bias protection circuit includes a high current discrete diode placed in series between the power source and the positive power supply terminal that connects the integrated circuits requiring protection. Accordingly, during a reverse voltage condition, the battery simply reverse biases the diode and protects the integrated circuits. The voltage drop across the diode, however, reduces the actual DC voltage available to the integrated.
Conventionally, a MOSFET driver is connected between the positive terminal of a device and a positive supply terminal as a high side voltage switch for reverse bias protection. During operation, when the MOSFET driver is conducting current, a positive voltage is connected to the positive terminal of the integrated circuit. When the MOSFET driver, however, is not conducting current during the reverse biased condition, the MOSFET driver provides reverse battery protection to the integrated circuit by shorting the positive supply voltage to ground through its backgate diode.
Most reverse battery protection circuitry, however, are designed to protect the components on the integrated circuit (IC) board or silicon chip alone, such that the electronics on board the IC would protect the rest of the electronics on board the IC. There are some applications, however, in which the reverse battery protection is necessary to protect external component connected to the IC. One such external component may be an external drive FET. Presently, there is no known design that will protect external components. During the reverse battery condition, if the external drive FET is not protected nor turned on, current path develops through the load and forward biases backgate diode of the external drive FET. As a result, a considerable amount of voltage is dropped across the external drive FET and, therefore, a considerable amount of energy is dissipated across the external drive FET, which is something most manufacturers desire to avoid. This power expenditure caused by the reverse battery condition affects functionality and reliability of the system including this IC and external drive FET.
As is displayed in FIG. 1, most automotive systems include a reverse battery protection circuit having a reverse blocking diode d6 placed in series with the load. As a result, the load is never energized. Thereby, no path exists for current to flow from the source to the ground plane depending upon the polarity. Yet, there are some applications that require that the load remain energized.
Thus, there is a need for a reverse battery protection circuit that provides an integrated reverse battery condition solution for protection of external NMOS switches during the reverse battery condition. This reverse battery protection circuit must minimize power consumption during a reverse battery event wherein there is no need for mechanical adjustments such as heat sinking and clamping to extract the heat away from the silicon and not destroy the device. There is a need for system modules that ensure a robust design for handling the increased power dissipation during the reverse battery condition.
The present invention is directed to overcoming, or at least reducing the effects of one or more of the problems set forth above.